Automatic gas regulating system



June 21, 1966 s s ET AL 3,256,900

AUTOMATIC GAS REGULATING SYSTEM Filed Jan. 18, 1965 2 Sheets-Sheet 1 Z4DEPOLARIZER GAS INERT GAS MIXTURE DEPOLARIZER id- GAS SUPPLY *2 vaDETECTOR CHOPPER V CIRCUIT, AMPLIFIER 2/ N V MIXING P /7 V CHAMBER A v14 32 3/ @Z.

INVENTORS NELSON N. ESTES KENNETH W. HANNAH CHARLIE D. ANDERSON CHARLESL. EVERSOLE BY L 2 ATTORN June 21, 1966 s s ET AL 3,256,900

AUTOMATIC GAS REGULATING SYSTEM Filed Jan. 18, 1963 2 Sheets-Sheet 2EEEE:

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INVENTORS NELSON N. ESTES KENNETH W. HANNAH CHARLIE D. ANDERSON CHARLESL. EVERSOLE BY dz]; A

ATTOR United States Patent 3,256,900 AUTOMATIC GAS REGULATING SYSTEMNelson N. Estes and Kenneth W. Hannah, Austin, Tex.,

and Charlie D. Anderson and Charles L. Eversole,

Bethesda, Md., assiguors to Union Carbide Corporation, a corporation ofNew York Filed Jan. 18, 1963, Ser. No. 252,377 6 Claims. (Cl. 137-88)This invention relates to a gas-regulating system. More particularly,this invention relates to a system for regulating the concentration of adepolarizer gas in a depolarizer gas-inert gas mixture.

By the term depolarizer gas as used herein and in the appended claims ismeant a gas possessing sufiicient electrochemical activity when actingon a carbon or metal electrode in a galvanic element to alter thepotential of the electrode in a reproducible manner. Typical depolarizergases possessing such activity are oxygen, the halogens, the nitrogenoxides, and the like.

The regulator system of the present invention is well suited to monitoror regulate the concentration of the aforedescribed depolarizer gases ina gas stream or a closed-system environment. The present regulatorsystem is particularly useful for continuous regulation of oxygenconcentration in diving units, space capsules, space suits, submarines,oxygen tents, and the like.

While the principle of utilizing the depolarizing properties of a gas asan indicator of the concentration of the same in a gas mixture is knownto the art, a need for a reliable regulating system capable of rapidresponse and reproducible results nevertheless exists. Prior art devicesdirected to this end rely on the continuous measurement of the currentor voltage output of a gas-depolarizable galvanic cell, however, such anapproach is plagued by uncontrollable variations in the resistance ofsystem components which in turn lead to erroneous output signals. Inaddition, the ohmic resistance of the sensing cell decreases the celloutput voltage in such instances.

It is an object of the present invention to provide a relatively simpleand reliable system for regulating the concentration of a depolarizergas in a given gas mixture.

It is a further object to provide a regulating system capable ofreproducible results in a wide range of environmental conditions.

It is another object to provide a regulatory system which relies on thetrue voltage of an electrochemical sensing unit as a depolarizer gasconcentration indicator.

These and other objects will become readily apparent from the ensuingdiscussion and the appended claims.

The aforesaid objects are achieved by a regulator which includes agalvanic sensing element containing a pair of electrically opposedgas-depolarizable cells, one of which is adapted for exposure to adepolarizer gasinert gas mixture and the other to a reference gascontaining a known amount of depolarizer gas. The true voltage outputfrom these electrically opposed cells is fed into a detector circuitadapted to produce a pulsating output signal in response thereto. Theresulting pulsating output signal is then fed to an amplifier, theoutput of which activates a suit-able control valve which in turnregulates the amount of a depolarizer gas added to a depolarizergas-inert gas mixture.

The invention will now be described in a greater detail with particularreference to the accompanying drawings, in which:

FIG. 1 is a block diagram of the regulating system;

FIG. 2 is a schematic view of a preferred circuit for determining thepotential difference of the gas-depolarizable cells of the galvanicsensing element; and

. izer gas supply 16 into a mixing chamber 17 via conduits 3,256,900Patented June 21, 1966 ICC FIG. 3 is a cross-sectional elevation of asuitable control valve.

Referring now specifically to FIG. 1, the regulating system comprises agalvanic sensing element 10 containing gas depolarizable cells 11 and12. The output signal of the sensing element 10 is fed into a detectorcircuit 13 Which produces a pulsating output signal. This pulsatingoutput signal constitutes the input of a chopper amplifier 14 whichproduces a direct current output signal in response thereto. The outputsignal from amplifier 14 activates a control valve 15 which regulatesthe amount of depolarizer gas passing therethrough from a depolar- 18and 23. The mixing chamber 17 also receives a depolarizer gas-inert gasmixture from a suitable supply 19 via conduits Z0 and 23. If desired,the flow rate of the gas mixture can be controlled by means of amanually operated valve 21. The concentration of depolarizer gas in thedepolarizer gas supply 16 is known; thus a portion of this gas isemployed as a reference gas and is passed through the gas-depolarizablecell 11 via conduit 22.

After passing through cell 11 the reference gas in conduit 22 is joinedwith gas in conduits 18 and 20 and fed into the mixing chamber 17through conduit 23. In this manner the gas mixture leaving the mixingchamber via conduit 24 contains the desired concentration of depolarizergas. Any concentration deviations of the gas in the conduit 24 aredetected by cell 12 and in the aforedescribed manner communicated to thecontrol valve 15 which then makes the necessary corrections indepolarizer gas concentration.

A suitable galvanic sensing element comprises a pair ofgas-depolarizable alkaline or acidic cells having their cathode elementsexposed solely to the monitored gas stream and a reference gas stream,respectively. For monitoring the oxygen concentration, the sensingelement cells can be composed of any two systems such asoxygen/C/KOH/Zn, oxygen/C/NaOH/Zn, oxygen/C/NH Cl/Zn, 0xygen/C/MgCl/Zn,'and the like.

The carbon cathode of one of the cells is exposed to the gas stream, theoxygen concentration of which is to be monitored, and the carbon cathodeof the other cell is exposed to a reference gas stream of a known oxygenconcentratiomusually a gas stream of substantially pure oxygen. Air canbe used as the reference gas in some applications, if desired.

Each cell generates a voltage varying with the oxygen partial pressureof the gas to which the cathode is exposed. The cells are connectedtogether electrically opposing each other .and the potential or voltagedifierential is measured by a detector circuit which includes loadresistors connected across each cell. However, during operation under aconstant current load, the internal (ohmic) resistance of each cellvaries in an irregular manner and thus produces variations in celloutput voltage even at a constant depolarizer gas concentration in themonitored gas stream. Such variations obviously greatly detract from theability of a system to give reproducible results and acceptablereliability. Moreover, variations of this nature cannot be tolerated indiving or space exploratory operations where a stable and reliablebreathing gas regulating system is of vital importance.

It has been found, however, that the variations due to the internalresistance of each cell as well as those due to varying conductivity ofcell contacts and leads because of drastic temperature changes,oxidation, etc., can be eliminated by the regulating system of thepresent invention. In the present system the cells are operated under apulse current load and the cell voltage differential is measured betweenconsecutive pulses. In this manner the potential drop across the ohmicresistance of the cell is eliminated and the true voltage generated bythe electrochemical processes within the cell can be measured. Shifts inthe depolarizer gas adsorption equilibrium on the cathode do not followthe rapid interruptions of current, and the cell output voltage betweenthe current pulses remains at a level corresponding to the averagecurrent flow during the preceding pulse.

In the instant system a pulsating current load can be applied by meansof a detector circuit shown in FIG. 2 where gas-depolarizable cells 11and 12 are connected so as to electrically oppose each other. Two loadresistors, 25 and 26, are connected in series and across bothgas-depolarizable cells 11 and 12, forming a conductive loop therewith.One of the load resistors preferably is a variable resistor which can beadjusted during calibration of the system. More than two resistors canbe used if desired. A transistor 27 is connected into the loop betweenthe cells 11 and 12 by means of its collector electrode and between theload resistors 25 and 26 by means of its emitter electrode. A pulsatingemitter bias current is provided by connecting the secondary of achopper transformer 28 across the emitter and base electrodes of thetransistor 27. This pulsating emitter bias current causes auni-directional pulsating current to pass through the cells 11 and 12during operation thereby polarizing the cells. This polarizing currentcan be adjusted by means of variable resistor 26, thus correcting forcell differences by load adjustment. The

differential output signal of the detector circuit can be measuredacross the aforesaid load resistors 25 and 26.

The voltage imposed on the cells by the polarizing current is a functionof the cell characteristics, the concentration range of the gas that isto be monitored, etc. In order to be able to calibrate the cells usinggas mixtures containing a low percentage of the depolarizing gas,preferably a small bias voltage of a suitable value is added to theoutput voltage of the sensing cell. For example, if the sensing cell issupplied with a 32 percent oxygen mixture and the reference cell issupplied with pure oxygen, a difference of 16 millivolts will existbetween the two cells. If a bias voltage of this amount is switched'into the circuit, the amplifier can be balanced to zero with these twogases; In the circuit shown in FIGURE 2, this is achieved by means of avoltage divider (resistors 33, 34, 35 and 36) connected to a suitableDC. power source 30 in series with a resistor 31 and stabilized by meansof a Zener diode 29. The imposed bias voltage can be regulated, ifdesired, by the variable resistor 32. FIG. 2 further shows means wherebygas mixtures having different predetermined depolarizer gasconcentrations can be monitored referring to the same reference gas.This can be achieved by providing a series of bleeder resistors 33, 34,35, and 36 that can be included in series with variable resistor 32 bymeans of the set-points 37, 38, and 39. In the aforedescribed detectorcircuit of FIG. 2 the output signal normally is measured across points40 and 41. In another variation of this circuit, resistors 34, 35, and36 can be replaced by a potentiometer and resistor 32 eliminated.

The pulsating output signal is fed into a conventional chopper amplifier14 indicated in FIG. 1 and having a DC. output. The input signal to thechopper amplifier is taken when the transistor 27 is in thenon-conducting state. This condition can be conveniently achieved byoperating chopper 28 180 degrees out of phase with the amplifierchoppers.

The direct current signal obtained from the chopper amplifier isemployed to activate a control valve 15 indicated in FIG. 1. Preferablythis valve has :a linear response to the DC. input signal over theentire operational gas flow range. A suitable valve for this purpose isshown in FIG. 3.

The control valve comprises a gas-tight housing 42 provided with a gasinlet 43 and a gas outlet 44. A permanent magnet 45 generating amagnetic field is rigidtration of the depolarizer gas both in thereference gasly positioned within the housing. An electromagnetic coil46 is mounted on a hollow core or armature 47 and suspended in theaforesaid magnetic field. To the core 47 is affixed :a valve stem 48which is adapted to mate with valve seat 49 positioned in gas inlet 43.In addition, a flexible member 50 such as a leaf spring, for example, isaflixed to the housing 42 and the valve stem 48 so as to bias the latterin the closed position. The extent of the bias is dictated by therequirements of the regulating system and its intended application. Theelecvtromagnetic coil 46 is energized by direct current obtained fromthe chopper amplifier output by means of contacts 51 and 52.

Prior to placing in service, the regulating system is balanced bypassing the reference gas through both cells of the galvanic sensingelement and adjusting a load resistor so that the output signal is zero.If the concenstream and the monitored gas mixture is to be the same,this is all the calibration that is necessary. However, since usuallythe reference gas is taken from the depolarizer gas supply which musthave :a relativelyhigher depolarizer gas concentration in order to be aneffective make-up stream, further calibration must be carried out. Thisis done by passing the reference gas through one of the cells and a gasmixture having the desired depolarizer gas concentration through theother cell. The sensing cell load resistor is then further adjusted byapplying an additional load to obtain a zero output signal. Followingthis the cell is ready for operation since any concentration deviationfrom the present one will result in an output signal. Once theregulating system is balanced, it can be set to monitor varyingdepolarizer gas concentration levels in gas mixtures by placingadditional resistors of predetermined values in the detector circuit asdiscussed above.

It will be understood that many changes in the details of constructionand the arrangement of parts and circuit components described herein maybe resorted to without departure from the scope and spirit of thisinvention.

We claim:

1. A regulator for a depolarizer gas in a depolarizer gas-inert gasmixture which comprises a galvanic sensing element containing a pair ofelectrically opposed gasdepolarizable cells, one of which is adapted forexposure to said gas mixture and the other to a reference gas containinga known amount of said depolarizer gas; circuit means for sensing thepotential difference of said cells and for producing a pulsating outputsignal; means for amplifying said pulsating output signal; a controlvalve responsive to the amplified signal; a depolarizer gas supply incommunication with the gas input side of said control valve; a referencegas delivery means communicating between said depolarizer gas supply andsaid one of said cells adapted for exposure to said reference gas; and amixing chamber adapted to receive said depolarizer gas-inert gas mixtureand the depolarizer gas metered through said control valve.

2. A system for regulating the concentration of oxygen in anoxygen-inert gas mixture which comprises a galvanic sensing elementcontaining a pair of oxygen-depolarizable sensing cells electricallyopposing each other, said cells being adapted for exposure to anoxygen-inert gas mixture and a reference gas containing a known amountof oxygen, respectively; circuit means for sensing the potentialdifference of said cells and adapted to produce a pulsating outputsignal; means for amplifying said pulsating output signal; a controlvalve responsive to the amplified signal; an oxygen supply incommunication with the gas input side of said control valve; a mixingchamber adapted to receive said oxygen-inert gas mixture and the oxygenmetered through said control valve; and a reference gas deliverymeanscommunicating between said oxygen supply and said mixing chamber forsupplying said reference gas to said cell adapted for exposure to saidreference gas.

3. The regulator in accordance with claim 2 wherein Said circuit meansfor sensing the potential difference of said cells comprises at leasttwo load resistors connected in series across said electrically-opposingsensing cells forming an electrically conductive loop therewith; atransistor having collector, emitter, and base electrodes connected intosaid loop between said sensing cells through the collector electrode andbetween said load resistors through the emitter electrode; and means forsupplying a pulsating emitter bias current connected across the emitterand base electrodes.

4. The regulator in accordance with claim 2 wherein said control valvecomprises a gas-tight housing provided with a gas inlet means having avalve seat and a gas outlet means, a permanent magnet rigidly positionedwithin said housing and generating a magnetic field, an electromagneticcoil mounted on a hollow core and suspended in said magnetic field, avalve stem affixed to said hollow core and adapted to seat within saidvalve seat, a flexible member afiixed to said housing and said valvestem biasing the latter in the closed position, and means for passingdirect current through said coil.

5. A system for regulating the concentration of oxygen in anoxygen-inert gas mixture which comprises a galvanic sensing elementcontaining a pair of oxygendepolarizable sensing cells electricallyopposing each other, said cells being adapted for exposure to anoxygen-inert gas mixture and a reference gas containing a known amountof oxygen, respectively; at least two load resistors connected in seriesacrosss said electrically opposing sensing cells forming an electricallyconductive loop therewith; -a transistor having collector, emitter, andbase electrodes connected into said loop between said sensing cellsthrough the collector electrode and between said load resistors throughthe emitter electrode; a chopper transformer secondary in series withthe resistors, connected across the emitter and base electrodes, andadapted to supply a pulsating emitter bias current; a bias voltage meansconnected across the sensing cell exposed to said oxygeninert gasmixture; a chopper amplifier having its input connected across bothsensing cells and said bias voltage means, receiving an input sign-a1when said transistor is not conductive, and providing an amplifieddirect current output; a control valve responsive to the amplifieddirect current output and providing a linear flow rate in responsethereto; an oxygen supply communicating with the gas input side of saidcontrol valve; a mixing chamber adapted to receive said oxygen-inert gasmixture and the oxygen metered through the output side to said controlvalve; and a reference gas delivery means for supplying said referencegas to said cell adapted for exposure to said reference gas and fordelivering said reference gas to said mixing chamber after passagethrough said cell, said reference gas delivery means communicatingbetween said oxygen supply and said mixing chamber and by-passing saidcontrol valve.

6. A pair of electrically opposed gas-depolarizable cells having acircuit constructed and arranged to sense the potential differencebetween said cells which comprises at least two load resistors connectedin series across said cells forming an electrically conductive'looptherewith; a transistor having collector, emitter, and base electrodesconnected into said loop between said cells through the collectorelectrode and between said load resistors through the emitter electrode;means for supplying a pulsating emitter bias current connected acrossthe emitter and base electrodes; and means for applying a bias voltageacross one of said cells.

References Cited by the Examiner UNITED STATES PATENTS 1,450,023 3/1923Edelman 137-93 X 3,001,757 9/1961 Ball 251-139 3,007,672 11/1961Tischler 251139 3,056,919 '10/ 1962 Kuipers 32430 3,086,169 4/1963 Eynon32430 ISADOR WEIL, Primary Examiner.

MARTIN P. SCHWADRON, Examiner. D. LAMBERT, Assistant Examiner.

1. A REGULATOR FOR A DEPOLARIZER GAS IN A DEPOLARIZER GAS-INERT GASMIXTURE WHICH COMPRISES A GALVANIC SENSING ELEMENT CONTAINING A PAIR OFELECTRICALLY OPPOSED GASDEPOLARIZABLE CELLS, ONE OF WHICH IS ADAPTED FOREXPOSURE TO SAID GAS MIXTURE AND THE OTHER TO A REFERENCE GAS CONTAININGA KNOWN AMOUNT OF SAID DEPLOARIZER GAS; CIRCUIT MEANS FOR SENSING THEPOTENTIAL DIFFERENCE OF SAID CELLS AND FOR PRODUCING A PULSATING OUTPUTSIGNAL; MEANS FOR AMPLIFYING SAID PULSATING OUTPUT SIGNAL; A CONTROLVALVE RESPONSIVE TO THE AMPLIFIED SIGNAL; A DEPOLARIZER GAS SUPPLY INCOMMUNICATION WITH THE GAS INPUT SIDE OF SAID CONTROL VALVE; A REFERENCEGAS DELIVERY MEANS COMMUNICATION BETWEEN SAID DEPOLARIZER GAS SUPPLY ANDSAID ONE OF SAID CELLS ADAPTED FOR EXPOSURE TO SAID REFERENCE GAS; AND AMIXING CHAMBER ADAPTED TO RECEIVE SAID DEPOLARIZER GAS-INERT GAS MIXTUREAND THE DEPOLARIZER GAS METERED THROUGH SAID CONTROL VALVE.